Many problems occur, such as static charges on the surfaces of the substrates of semiconductors, liquid crystals, and organic EL, causing their circuits to break. The charges are built up on the surfaces when manufacturing or handling them. In addition, the charges of the substrates cause some dust to adhere on the surfaces.
To solve these problems, an ionizer is provided for each manufacturing device for semiconductors, liquid crystals, or organic EL, so as to prevent or remove the static charges on the surfaces of the substrates. There are two types of ionizer. One is an electric ionizer, in which the air is ionized by applying a high voltage to it. The other is an ionizer using soft X-rays, in which the air is ionized by irradiating it with soft X-rays.
As a prior patent publication on a remover using soft X-rays that removes the static charges, Japanese Patent Publication No. 2001-257096 (prior patent publication 1) is known.
The electric ionizer is easy to handle, but has some problems such as the wear of the electrode caused by discharging it at a high voltage for a long time. Thus, the electrode must be replaced. It also has problems such as dust being generated and adhering to a substrate.
The electric ionizer has further problems such as harmful effects being caused on the substrates by oxidizing or deteriorating them because it generates a great amount of ozone.
On the contrary, the ionizer using soft X-rays does not generate ozone. Thus it is a clean ionizer. However, it has a problem in that it must have a structure that prevents soft X-rays from leaking outside, because soft X-rays have harmful effects on a human body.
Ionizers using soft X-rays in which only ionized air is taken out, and without leaking soft X-rays, have been developed. However, all of them have problems such as the portion for blowing out ionized air being complicated and large, and the passage for the ionized air being difficult to be curved or shortened. Thus, it has been difficult to efficiently take out a great amount of ionized air.
Prior patent publication 1 discloses the following embodiment. A tube for soft X-rays is installed in a fan-filter-unit to generate ions inside the unit. Two plates with punched holes are disposed at the side for blowing out the ionized air. They are stacked with a clearance of 3 mm so that the openings of one plate do not overlap those of the other. A honeycomb sheet is further stacked on them. By doing so, only the ionized air is blown out, and no soft X-rays leak. Then the time for removing static charges from a charged article is measured.
However, the ionizer of prior patent publication 1 has problems such as an insufficient performance to block soft X-rays and a long time being necessary for removing static charges from a charged article. Thus it does not comply with the requirements from the manufacturers for shielding soft X-rays and shortening the time for removing the static charges from a charged article in the present removers.
The recent requirements from the manufacturers of liquid crystals and semiconductors have become more severe. They strongly request that the functions to shield soft X-rays be enhanced so that their leakage is further reduced or becomes almost zero, to safeguard operators.
To comply with such requirements from the manufacturers in regards to the functions, the need has arisen to fundamentally rethink the ways to block soft X-rays and take out ions. The present invention was made in view of such requirements. It provides a sheet for shielding soft X-rays to prevent them from leaking from the port for discharging the ionized air. The soft X-rays that enter the sheet from the port for supplying the ionized air hit at least three times before reaching the port for discharging the ionized air. Thus, their travel in a straight line is prevented. So they can be attenuated or made to disappear.